A conventional tower crane as shown in FIG. 7 includes: a jib J horizontally rotatably mounted on a top portion of a lattice tower L about a slewing axis S, a trolley T slidably held on the jib J for hoisting use, a counter balance such as concrete slab W mounted on an opposite end of the trolley T, a control cabin C positioned on an upper portion of the lattice tower L, and a base B loaded with base weights and secured on a ground or floor surface.
However, such a conventional tower crane when used for the construction of a tall building may have the following drawbacks:
1. The jib J has a limited length and rotating radius about the slewing axis S, thereby limiting a working or hoisting area by the tower crane. For a larger construction site, several tower cranes must be provided to increase the construction cost.
2. The lattice tower L and the crane base B will always occupy a space within a building or in the building construction site. It requires professional skill for adjusting the height of the tower crane.
3. If the tower crane is erected within the building, a void space should be remained in the building for locating the tower crane for hoisting purpose. After completing the building construction, a further work to "re-fill" the void space in the building is required, possibly delaying the construction time schedule.
4. The crane operator should always stay in the cabin C which is located at a very high position, easily causing tiredness and danger to influence jib safety for the operator. For ensuring the safety for the operator and other workers, the labor insurance fees will be greatly increased to cause a heavy burden. The present inventor has found the drawbacks of the conventional tower crane, and invented the building crane apparatus having improvements over the conventional crane.